A process for manufacturing semiconductor devices from a wafer includes various processing steps, and each of the processing steps is performed on the wafer mounted on a mounting table. An alignment operation for precisely positioning the wafer is often performed prior to a specific processing step to be performed on the wafer.
In case a wafer is inspected by an inspection apparatus shown in FIG. 5 for example, the alignment between a plurality of test electrodes of each device of the wafer and probes corresponding thereto is performed before the inspection is carried out by allowing electrical contact between the test electrodes and the corresponding probes. As illustrated in FIGS. 5A and 5B, the inspection apparatus includes a loader chamber 1 for loading and unloading of a wafer W; and a prober chamber 2 for inspecting electrical characteristics of the wafer W. The loader chamber 1 has a transfer arm 3 for transferring a wafer W in a cassette C to the prober chamber 2; and a pre-alignment mechanism 4 for performing a pre-alignment of the wafer W while the wafer W is being transferred by the transfer arm 3.
The prober chamber 2 has a mounting table 5 for mounting thereon the pre-aligned wafer W, the mounting table 5 being movable in X, Y, Z and θdirections; a probe card 6 disposed above the mounting table 5; and an alignment mechanism 7 for performing an alignment between a plurality of probes 6A of the probe card 6 and the wafer W on the mounting table 5. Further, the probe card 6 is fixed at an opening of a head plate 8. A test head 9 is provided on top of the head plate 8, and the probe cared 6 is electrically connected with a tester (not illustrated) via the test head 9.
The pre-alignment mechanism 4 has a rotatable table 4A for mounting thereon the wafer W; and an optical detection unit (not shown) for optically detecting notches formed around an outer periphery of the wafer W. While the rotatable table 4A having thereon the wafer W is rotating, the optical detection unit detects the notches of the wafer W, thereby pre-aligning the wafer in a specific direction. As for a pre-alignment mechanism of the kind described above, there is known a wafer pre-alignment mechanism described in Japanese Patent Laid-open Application No. H10-012709.
As depicted in FIGS. 6A and 6B, the alignment mechanism 7 has a first CCD camera 7A for capturing images of the wafer W; a second CCD camera 7B, attached to the side of the mounting table 5, for capturing images of the probes 6A; and an alignment bridge 7C for supporting the first CCD camera 7A; and a pair of guide rails 7D for guiding the alignment bridge 7C to a probe center. The first CCD camera 7A captures the images of the test electrodes of the wafer W, and the second CCD camera 7B captures the images of the probes 6A. Next, the test electrodes and the probes 6A are aligned based on the image position data.
Prior to the alignment of the wafer W, a size and a center of the wafer W are detected by using the first CCD camera 7A. That is, while the mounting table 5 is translationally moving under the first CCD camera 7A, an image of the wafer W is captured and processed, thereby recognizing three points on the circumference of the wafer W as points P1, P2 and P3, as shown in FIG. 7. Next, a line segments P1P2 and P2P3 are obtained by a computer and, then, an intersection point of the perpendicular bisectors of the respective line segments is calculated as the center C of the wafer W.
However, in a conventional method of detecting the center C of the wafer W, the mounting table 5 needs to be moved so that the circumferential portion of the wafer W can cross an optical axis of the first CCD camera 7A in order to allow the three points P1, P2 and P3 of the wafer W to be recognized by the first CCD camera 7A. As a consequence, a moving amount of the mounting table 5 increases, and a long period of time is required to detect the three points, which hinders the reduction of time for aligning the wafer W.